1. Field of the Invention
The present invention generally relates to an apparatus for controlling operation of an internal combustion engine (hereinafter also referred to simply as the engine) by controlling fuel injections, ignition timings and the like for the individual cylinders of the engine On the basis of a reference position signal and/or cylinder identification signals. More particularly, the invention is concerned with an engine control apparatus which is equipped with a back-up capability or function which allows the engine operation control to be performed even when failure or fault or abnormality in more general term should occur in the cylinder identification signals or the reference position signal.
2. Description of the Related Art
In general, in the internal combustion engine for an automobile or motor vehicle, it is required to control optimally the fuel injection and the ignition timing in accordance with the operation state of the engine or motor vehicle. In conjunction with such control, a microcomputer is employed for identifying discriminatively the reference angular position of a crank shaft of the engine on a cylinder-by-cylinder basis to determine through calculation the ignition timings for the individual cylinders, respectively.
FIG. 12 is a block diagram showing an engine control apparatus known heretofore which is configured so as to perform a group-wise ignition timing control for two cylinder sets each including two cylinders in an engine having four cylinders.
Referring to the figure, there are provided as signal input means a reference position signal generating means 1 for generating a reference position signal T corresponding to a reference crank angle position on a cylinder-by-cylinder basis in synchronism with rotation of an engine (not shown) and a cylinder identification signal generating means for generating a cylinder identification signal C for identifying individual cylinders in synchronism with rotation of the engine. Each of the reference position signal generating means 1 and the cylinder identification signal generating means 2 is constituted by a rotatable slit disk mounted on a crank shaft or a cam shaft interlocked thereto and photo-detectors disposed in opposition to the rotatable slit disk, as described hereinafter in more detail.
The reference position signal T and the cylinder identification signal C are inputted to a control means 3 which can be implemented by using a microcomputer and which is adapted to detect the reference positions of the individual cylinders on the basis of the reference position signal T and the cylinder identification signal C and calculate the ignition timing or the like control parameters in accordance with the operation state of the engine to thereby output a control signal (ignition coil turn-on/off signal) for controlling the ignition timing.
An ignition coil 41 is provided in association with a set of cylinders labeled #1 and #4, while an ignition coil 42 is provided in association with another set of cylinders labeled #3 and #2. Electrical energization and deenergization of these ignition coils 41 and 42 are controlled by the control signal generated by the control means 3.
The control means 3 includes input interface units 31 and 32 for shaping (or conditioning) and fetching the reference position signal T and the cylinder identification signal C, respectively, a timing control unit 33 for calculating the ignition timings for the individual cylinders on the basis of the reference position signal T and the cylinder identification signal C in accordance with the operation state of the engine, and output interface unit 34 and 35 for outputting control signals corresponding to the ignition timings to the ignition coils 41 and 42, respectively.
FIG. 13 is a perspective view showing typical structures of the reference position signal generating means 1 and the cylinder identification signal generating means 2. Referring to the figure, a slit disk 11 which may also referred to as the signal disk is mounted on a cam shaft 10 which is rotated in synchronism with the rotation of the engine. A plurality of slits 12 and 13; 14 are formed coaxially in the signal disk 11 in the direction in which the disk 11 is rotated, wherein the radially outer slits 12 (four arcuate slits corresponding to four cylinders, respectively, and having a same length) are adapted to partake in generation of the reference position signal T for the individual cylinders, while the radially inner slits 13 and 14 of different lengths (two slits corresponding to the two cylinder sets, respectively) are adapted to generate the cylinder identification signal C for identifying the cylinder sets.
A pair of light emitter elements 15 and 17 are disposed in opposition to a pair of light receiving elements 16 and 18, respectively, wherein a peripheral portion of the disk 11 having the slits 12, 13; 14 formed therein is interposed between the light emitter elements 15; 17 and the light receiving elements 16; 18. Thus, the light emitting element 15 and the light receiving element 16 cooperate to constitute a photo-detector disposed in opposition to the trace of the slits 12 for generation of the reference position signal T, while the light emitting element 17 and the light receiving element 18 constitute a photo-detector disposed in opposition to the path of the slits 13 and 14 for generation of the cylinder identification signal C.
FIG. 14 is a timing chart which illustrates the reference position signal T and the cylinder identification signal C together with a coil current having a waveform I1 for the ignition coil 41 provided in association with one set of cylinders and a coil current having a waveform I2 for the ignition coil 42 associated with the other cylinder set. As can be seen in this figure, the reference position signal T includes pulses each having a leading edge rising up at a crank angle of B65.degree. (indicating a crank angle 65.degree. before the top dead center or TDC) of each cylinder and a trailing edge falling at a crank angle of B5.degree., wherein the position corresponding to the crank angle of B65.degree. is referred to as the reference position with the position corresponding to the crank angle of B5.degree. being termed the initial reference position. In terms of the crank angle, the total period of the reference position signal T for the four cylinders amounts to 720.degree., wherein one pulse period for each of the cylinders corresponds to 180.degree.. Further, the pulse width or duration extending from the reference position B65.degree. to the initial reference position B5.degree. corresponds to 60.degree. in terms of the crank angle, and a pulse quiescent duration intervening the initial reference position B5.degree. for a given one cylinder and the reference position B65.degree. for the cylinder succeeding to that given one cylinder corresponds to the crank angle of 120.degree..
On the other hand, the cylinder set identification signal C contains pulses of different waveforms which differ in phase from the pulses contained in the reference signal position signal T so that the signal C have a different signal level at the reference position B65.degree. and the initial reference position B5.degree. for the individual cylinder sets. By way of example, by imparting such waveforms to the pulses of the cylinder identification signal C that one pulse corresponding to one cylinder set assumes a signal level "1" at both the crank angle positions B65.degree. and B5.degree., while the succeeding pulse corresponding to the other cylinder set assumes levels "1" and "0" at the positions B65.degree. and B5.degree., respectively, it is possible to identify discriminatively the particular cylinder sets from each other. Generation of the pulses of the waveforms mentioned above can be realized by appropriately designing the slits 12 and 13; 14.
Next, description will turn to operation of the known engine control apparatus shown in FIG. 12 by reference to FIGS. 13 and 14.
When the engine rotates, the reference position signal generating means 1 constituted by the combination of the photo-elements 15 and 16 and the slits 12 and the cylinder identification signal generating means 2 constituted by the combination of the photo-elements 17 and 18 and the slits 13 and 14 generate the reference position signal T and the cylinder identification signal C which have waveforms such as illustrated in FIG. 14, respectively. These signals T and C are supplied to the timing control unit 33 incorporated in the control means 3 through the input interface units 31 and 32, respectively.
On the basis of the reference position signal T and the cylinder identification signal C, the control unit 33 detects the reference positions for the individual cylinders to thereby calculate the control quantity for controlling the ignition timing in dependence on the engine operation state, as a result of which the control signals for controlling the ignition timings are outputted from the control means 33 through the output interface 34 and 35 to be applied to the switching elements provided in association with the ignition coils 41 and 42, respectively. In that case, when the ignition timing is to advance, the timing control is performed with reference to the reference position B65.degree., while when the ignition timing is to lag, the timing control is then performed with reference to the second reference position B5.degree..
The conventional engine control apparatus described above suffers from a serious problem that when either one of the reference position signal T or the cylinder identification signal C becomes abnormal or unavailable due to occurrence of a fault or failure in either one of the two signal channels composed of the photo-detectors 15; 16 and 17; 18 and the slits 12 and 13; 14, respectively, it becomes impossible to perform the cylinder identification or the detection of the reference position, leading to functional disability or malfunction of the timing control unit 33. To say in another way, because the conventional engine control apparatus generates the engine operation control signal on the basis of the reference position signal T and the cylinder identification signal C, there may arise such unwanted situation that the engine control is rendered impossible when abnormality occurs in either one of the reference position signal (T) channel or the cylinder identification signal (C) channel. In this conjunction, it is safe to say that the possibility of simultaneous occurrence of abnormality in both the signal channels can be neglected in practical applications.